Which of the following instruments is most suitable for measuring the outside diameter of a narrow pipe in a few millimeters in diameter?

Analysis

The question asks for the most suitable instrument to measure the outside diameter of a narrow pipe (a few millimeters in diameter). Precision is the key factor here because the object is very small.

Concept Explanation

In physics, the choice of a measuring instrument depends on the precision required and the size of the object:

• Meter rule: Used for general measurements (precision of 1 mm). It is not suitable for small, curved surfaces like a narrow pipe.
• Tape rule: Used for long distances (precision of 1 mm). It is too bulky for a small pipe.
• Pair of calipers (Vernier Calipers): Used for measuring internal and external diameters with a precision of about 0.01 cm or 0.1 mm.
• Micrometer screw gauge: This is a high-precision instrument designed specifically for measuring very small objects (like the thickness of a wire or the diameter of a small pipe) with a precision of 0.01 mm.

Step-by-Step Solution

1. Evaluate the object: A "narrow pipe" with a diameter of only a few millimeters is a very small object.
2. Compare precision: • A meter rule and tape rule are too imprecise for millimeter-scale measurements. • Vernier calipers are good, but a micrometer screw gauge is specifically engineered for high-accuracy measurements of small, cylindrical objects.
3. Determine the best fit: Because the micrometer screw gauge has a much smaller least count (0.01 mm) compared to the others, it provides the most accurate and reliable reading for a narrow pipe.

Conclusion

The micrometer screw gauge is the standard laboratory instrument for measuring small diameters with high precision.

Exam Tip: Always remember the "Least Count" rule:

• Meter rule: 1 mm
• Vernier Calipers: 0.1 mm
• Micrometer Screw Gauge: 0.01 mm If the question asks for the "most suitable" or "most accurate" for small objects, always go for the one with the smallest least count!